Vacuum sealed solar panels?

[Jeff7]

I've searched for this, without finding anything substantial, so here goes.

I have read about homemade panels developing moisture problems. This is sometimes solved by sealing the panel, however, this can lead to the buildup of high pressures when the panel is heated, possibly damaging various components.

So I'm wondering about adapting something like this to a panel, to suck some of the air out (not all, as this might crush some slightly curved solar cells), thus allowing room for the air in the panel to both expand and contract. With less air, in winter, the panel could still contract, without causing anything harm, and in summer, it could expand without causing explosive pressure.

Thoughts on this? Has this method been attempted before?

[Jeff7]

Wanted to add too, yes, I'm another buyer of those fine EvergreenSolar solar cells from eBay. My sister's in college in that area; maybe one time when she's making a trip between here and there, I'll do the driving, and make a stop off at Foxboro, and pick up some cells in person, and hopefully avoid breakage.

I just got a pound of the things, and here's the breakdown:

286. grams good (30 cells)
     
180. grams cracked
     
     

That's close to a 40% breakage rate. A lot of them had hairline cracks, which I found by lightly twisting each cell, listening for the high-pitched grinding of silicon on silicon. Most of the breaks were the bad vertical ones, across all the crossconnects. However, I did still wind up with a lot of sizable scrap pieces, which means that I have plenty for experimentation. I intend to make a small prototype with a few of these cells. Then I can also decide if it's worth a drive up to Boston from east-central Pennsylvania, plus the monetary investment of a few hundred dollars for more solar cells.

[tecker]

Removing all the air will work but the vacumm process pulls in on the Glass so this has to be a acounted for. If you try this post your results . I think that bringing the panel up 250 F with one end open and sealing then this will remove 90% of the moisture from the air that remains inside a a slight vaccum will exist after and the sealent will dry quickly  but you have to keep the temp above 200. Alittle silica gell packet at one corner can remove the rest .

[Ungrounded Lightning Rod]

Sucking out the air reduces the heat transfer, and losing heat is the big issue for solar cells.  Their output drops when hot.

I understand the main issue with deterioration is moisture.  If I were doing them I'd think about this:

 - Stick 'em to a metallic backing with an insulating barrier and two layers of heatsink compound.

 - Throw a little freshly-charged silica jell into the panel before sealing it.

 - Seal it in a hot dry environment (easy for me, with the desert house).

 - If I'm feeling fancy, purge it with dry nitrogen or canned dry air just before sealing it.

[pyrocasto]

I never thought of any of that.

I was going to let my panel get hot, open it up, and close it. But are there any other gasses that would not expand so much?

Also, instead of silicone I was going to use a rumber gasket around the edge. Would that now work?

[iFred]

Seems silica is all the rave, but is it? Nope I don't thing so. The problem is that the silica will indeed pull in moisture, but ask yourself where that then goes? Unfortunately the moisture ends up in a single place now, in the silica, which as soon as the temp rises or falls or the humidity changes or what ever the silica will release the moistures  and thereby causing the problem again. The idea of silica is actually a good one if it could eat the moisture or something, but it does not, it stores it, and that can only lead to more problems.

 

[tcrenshaw]

I'm using helium and it seems to work well. After mounting the glass against the panel using insulation seal AKA: weather stripping, I punch two small holes in the bottom of the seal with a hot soldering iron. I insert the tube for the helium into one hole, tilt the panel up and open the valve allowing the helium to enter the panel slowly. Since helium is lighter than air it goes to the top of the panel, pushing the air out the bottom. Hold a match, candle, lighter..etc near the open hole at the bottom where the air is coming out. When you see the flame go out, helium is escaping. I only had to do this a few times and learned how long it takes to fill a panel. Close the valve, remove the gas tube and plug the two holes. I use wooden dowels to plug the holes with. Since I'm sure I don't have a solid or perfect seal around the glass eventually the helium will escape. Using the plugs in the holes allows me to do this procedure at a later date if moisture becomes a problem again. Also since it's not a perfect seal, there's no worry about pressure build up when the helium expands in the sun light. Unfortunate part is of course that when it contracts it will pull in regular air and moisture, but that'll all be at the bottom of the panel.

The problem? Helium isn't that cheap. Well the helium is cheap, it's the disposable bottle that it comes in that costs. I don't know if I'll continue with this process. I have two panels that are open air with four vent holes. They do see some condensation but it doesn't seem to be a major issue, yet. One has the silica pack in it mentioned above, the other does not - no visible difference. I'm no longer putting the silica packs in.

I have modified my design since my first panel. My first panel worked great for a few days and then needed to be dis-assembled because of an over heating problem. It was a nightmare to pull apart (was completely silicon sealed). Now I can pull my panels apart if need be.

[RatOmeter]

Just pondering it and I'd think it would be better than nothing.  Best to dry the silica packet in low heat for an hour or so, to be sure it's as dry as possible before installation.

Another thought for those with Mig or Tig rigs (sorry for the alliteration), how about using welding gas (argon/argon mix) to purge the panel (I'm assuming it's quite dry)?

[Jeff7]

I wasn't looking to use glass for this - I was looking at polycarbonate. Glass...for one, I don't know that there are many good places around here to get sheets of it, and second, it's not easy to cut accurately. PC can be cut with a bandsaw.

I'm also hoping to use two sheets of PC per cell - the one extra sheet will be on standoffs, away from the main panel, as a shield against hail and other flying objects. It would also be removable and replacable, should it suffer serious damage. Granted, I might get slightly lower output from two sheets of PC, but it should be worth it if I don't have to replace an array from impact damage. I'll test just how much output I do lose, when and if the sun ever shines here again; it seems like it's been cloudy non-stop since sometime in November.

And I am not going to remove all of the air - I said I only wanted to remove some of the air, and just make it low pressure, not a vacuum. Maybe I should have put "Low pressure sealed" in the title instead of vacuum.

But if only some of the air is removed, then there's not enough outside pressure to crush the cells, while at the same time, allowing for the air inside to heat and expand, without popping the entire assembly apart.

I would also like to use a metallic backing on these cells, to serve as a heatsink. I'm thinking maybe a sheet of steel (that'd be pretty heavy though) or aluminum, with cross supports for rigidity. Maybe I could use a dab of thermal adhesive on the back of each cell, or maybe something like this, maybe 5 of them per cell - 4 corners, and the center. Or a combination of both adhesive (center dab) and 4 thermal pads.

[picmacmillan]

here is something i just came up with about moisture and condensation......when we go moose hunting in the north we build a shack out of plastic......if you used just one layer of plastic the tent will drop condensation all over the place when you turn on the wood stove  but we use 2 sheets of plasic and the condensation runs between the two and we have no problem with it on the other side where we are living.....i am going to take one of my homebuilt panels and try using an extra layer of clear plastic or glass just to see what may occur...i beleive from past practice the moisture can be diverted in this fashion....pickster

[ghurd]

Someone here not long ago took their panels to a glass shop and had them filled with gas and sealed.  Just like a thermopane window. Cost effective. He was happy.

Sounds like a winner of an idea to me.

Six or eight weeks ago? Wish I could remember who it was.

G-

[iFred]

I think the vacuum out and insert inert gas into space is a good one. The problem is keeping a vacuum and leaking of the gas. Plastics for fact do not do this well, they vent semi rapidly, the molecular structure is not designed for this. The second problem is bending. As the vacuum begins the plastic or glass will bend inward with the high probability of breaking the cells. I use 3/16 " spacers in my panels which are made of the tempered glass to avoid bends or other problems. If you visited my web site you will note the spacers placed evenly. Hope this helps.

[pyrocasto]

So what about two piece of glass(like yours), with some kinda seal on the outside, and spacers everywhere. Could you just take it to the glass shop and have it turned into a thermopane window like ghurd said?

[Jeff7]

This is probably the page you mean.

Wonder what kind of "glass place" he means?

That does sound like a good idea though; it'd be professional grade sealing then, and with inert, dry gas.

If I knew of a place like that nearby (I did inquire in that thread there as to the name/type of place it is), and a source of cheap glass, that sounds like a good way to go.

When everyone says "auto glass place" or something along those lines, what do you mean specifically? What are some store names I can look up? I'm afraid I really don't know the first thing about acquiring materials outside of conventional channels like retail stores.

[picmacmillan]

i just called a window factory and they didn't seem to enthusiastic or knowledgeable about gases either inert or not....i actually had to let him know that krypton and argon are group 7 gases on the periodic table which means they are not explosive like group 8.....anyhow,i would be interested to see where we could get such gases as individuals and i would have to refresh my memory or go back to my physics and engineering books to see what properties we are especially looking for in  this gas...one more note is the saleman said they use krypton gas...maybe this is cheaper to use than argon, or radon but that is just my assumption....pickster

[ghurd]

Not the right thread.

I believe the right one was very specific and even told how he got the wires to the outside of the panel.

I would start with the phone book under glass. Then auto glass, then windows.

Just tell them you need a 'custom thermopane window', and they will get you to the right person. Then you can fill in the guy who can understand what you are talking about.

Big and small shops is where I have the best luck with unusual needs. Big shops have the people and equipment. Small shops specialize.

Medium sise shops tend to be the least helpful in my experiance, trying only to move large quantities of common product.

If they can't help you, ask them who can.

It would probably be helpful to just look for hours to find the right thread, and print it for the glass shop when you go.

G-

[BrianK]

i think most of the gas that is used for that is argon.

 

[jimjjnn]

By using a vacuum you may actually increase heating of solar cells as heat will not reradiate out of the front glass as readily thereby increasing temp of your cells. Not a good thing.Vacuum is used in hi-temp water heating tubes for solar water heating. That is the reason for a vacuum. It holds the heat in.

[tecker]

  Running the Temp up seems to get rid of all the moisture I've been getting the temp to top 250 F with a panel heater (commonly used for a dehumidifier in a nema 4 encloser) for 20 minutes and locking down the seal no moister buildup at all between test cycles.Testing for warping and new cracks before final assembly . I've purchased

  smooth on c1508 ( the directions suggest curing first at room temp then above 200 for two hours and then above 250 for 2 hours)for a backing to bed the cells into ( transfers heat really well ) and fills in the spaces under the cells . I've gone through 6 lbs testing and will start to assemble shortly .

[jimjjnn]

There are thin shhets of heat sink mylar that is used in heat sinks .Smear heat sink grease   on both sides of mylar and put mylar sheet on metal back panel (copper sheet or aluminum). Then put your cells on that and press very gently with front glass .

Heat then can radiate through the back panel to air on the back which is cooler as it is always in the shade.

[jimjjnn]

I forgot one thing. Don't get heat sink grease at places like Radio Shack as those little tubes won't go very far. Call electronic supply houses and they should be able to tell you where you can get larger amounts a lot CHEEPER.

Another thing that may help too. The mylar survival blankets may work if they are non-cunductive. I understand they are CHEEP and they will also reflect heat .

[jimjjnn]

Wish I could get all my thoughts together in one rush instead of bits and pieces. The heat sink grease also may keep moisture from getting to the cells. Don't know for sure but might be worth trying.

I thimk I ran my head dry on that one. I hope

[jimjjnn]

What do storm window mfrs

use between home storm windows glass?2 sheets of glas with an inert gas. between Gotta be CHEEP !

[Joel]

I believe the problem with argon is it has some property that helps block certain UV rays which is why glass window manufactures use it.  Should be readily available at any welding supply shop.  As we know, the way in which solar panels work requires as many different rays as possible to get maximum efficiency.  Personaly, I'm working with helium due to availability.

Joel

[jimjjnn]

Argon has very little blocking of light.

It is the metallic "E" coating that blocks infra-red and UV light

[Joel]

Then the argon must inhibit heat transfer.  I see no other reason manufactures would use it if it did not contribute in some way to the efficiency of the window.  I would believe that air-driers would be cheaper than argon gas on an industrial scale.  Either way, I tends to think argon is a bad choice.

Joel

[RP]

All you never really wanted to know about argon:

Argon has four properties that are good for window making.

1.  Its relatively cheap because it can be condensed out of the air (air is about 1%argon)
   
2.  Its inert so it doesn't react chemically at all with the glass or the sealing materials.
   
3.  Its a relatively large atom so it doesn't diffuse out through the sealing materials as fast as a small molecule will.
   
4.  Also because its a heavy atom it is not as efficient at transfering heat through conduction.  
   
   

Picture an extremely magnified cross section view of a thermal window.  Light weight gas atoms or molecules are bouncing around at very high speed like ping pong balls on a speaker cone.  Every time a gas atom bounces off one pane of glass (the warm one) it picks up a small amount of heat.  When it bounces off the other pane it gives up some to the cooler pane of glass.

A heavy gas atom or molecule moves slower at the atomic level and so does not carry the heat between the glass panes as efficiently.  Argon has an atomic weight of ~40 so its quite massive compared to hydrogen with an atomic weight of 2.  Hydrogen gas is normally found in the form of H2 (two atoms stuck together) so the molecular weight is 2 compared to 40 for argon (being inert, argon doesn't form molecules).

In fact hydrogen is one of the best gasses for thermal conductivity and this is why all commercial power generators (in power plants) are purged with it during operation because its the best way to transfer heat from to rotor out to the stator to get rid of it.

Actually Krypton or Xenon would be much better than argon but they are both rare and therefor much more expensive.

Going back to helium again, its atomic weight is 4 so its a fairly decent conductor of heat but its not as cheap since you really only get it from natural gas.  The big problem is helium's ability to diffuse through many materials.  This is why a rubber balloon filled with helium will get smaller in a day or two and stop floating as well.  The helium diffuses right out through the rubber (air also diffuses inward but not as fast).  The aluminized mylar baloons present a better barrier which is why they last longer.

As far as a gasses for filling solar panels go, argon would be a good one but actually plain old dry air should be just as good since thermal insulation isn't really an issue when both panes of glass are outside.  You can make dry air by making an inline canister filled with baked out dessicant (available in craft shops for drying flowers) and feeding it with an aquarium air pump.

Don't ask me what time it is or I'll tell you how to build a clock.  :-)

rp

[Jeff7]

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Don't ask me what time it is or I'll tell you how to build a clock.  :-)

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Hey, a detailed explanation is a good thing; details help those of us who aren't in the know.

The thing with there being other, better gases is like a problem with computers, or electronics. Sure, gold conducts power great, and resists corrosion well. Natural diamonds are very strong. But they're just too hard to get, and so not feasible. Argon was apparently the best balance of cost vs performance, so it is used.

So these glass places, they would stock tempered glass, and be able to make a custom sealed assembly with the solar cells inside? I'll have to look into that, and get an idea of prices. If I can make solar panels at a decent price, I just might have to drive up to Massachussets (my sister goes to college there anyway, and pick up lots of solar cells in person. Hopefully I can get a lower breakage rate that way - I don't know how many are damaged in shipping, and how many leave the seller's place that way.

I'd probably have to get the tempered glass from the glass place, take it home, get the cells attached and ready to go, and bring it back for wiring. I'll have to inquire about the sealing process - the wires have to get to the outside of the panel somehow.

Do you think I should wire a diode with the panel right away, or leave that external to the thing? I read about diodes blowing out, so I'm thinking that keeping it external might be a good idea.

[iFred]

Even with the best silicon that I could buy, I think it's still going to leak a gas. I could be wrong. Dnn't know till you try I suppose.

[iFred]

How about helium. Balloon tanks , they are rentable and besides you can also talk like donald duck when you are done!

[ghurd]

A vacume will be trying to draw in air. A gas filled void will be close to 1 atmosphere.

I'd go with the window makers.

Did not know where this fits in here, so here it is.

G-

[tecker]

I think you'll find Urethane sealant in use by most window installers very good stuff but slow dring

[iFred]

Her is what I was thinking would help to make a good seal all the way around. It is almost identical to the way in which standard dual pane glass is put together. The difference is that the glass does not touch the aluminum channel. The slight squeezing the two glass sheets would be enough I believe that the entire thing if siliconed in would be air tight and would find it hard to leak. The channel does go all the way round the glass.